Synthesis and Characterization of <i>β</i>‐Diketiminate Aluminum Compounds and Their Use in the Ring‐Opening Polymerization of <i>ε</i>‐Caprolactone

Ma, Xiaoli; Yao, Miaomiao; Zhong, Ming; Deng, Ziyan; Li, Wenling; Yang, Zhi; Roesky, Herbert W.

doi:10.1002/zaac.201600396

Cited by 9 publications

(6 citation statements)

References 53 publications

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“…The Al–Me bond length in complex 2 [1.943(2) Å] is virtually identical with that observed for 16 Fnac 2 AlMe 2 [1.945(2) Å], but shorter than those reported for 10 Fnac 2 AlMe 2 [ 10 Fnac 2 = HC[C(CH 3 )NC 6 F 5 ] 2 , 1.957(3)/1.947(3) Å] [ 23 ] and Mesnac 2 AlMe 2 [1.960(3), 1.966(4) Å], [ 24 ] respectively. As was observed in the zinc complexes, the Al–N bond length also increases and the N–Al–N bond angles decrease with decreasing σ ‐donor capacity of the β ‐diketiminate substituent [Mesnac 2 AlMe 2 1.916(3)/1.926(3), 95.24(12)°; [ 24 ] 10 Fnac 2 AlMe 2 1.917(2)/1.926(2), 94.00(8)°; [ 23 ] 16 Fnac 2 AlMe 2 1.948(2)/1.942(2), 93.02(7)°; [ 19a ] and 17 Fnac 2 AlMe 2 (1.949(2)/1.956(2), 89.80(8)°], whereas the Me–Al–Me bond angles steadily increase [Mesnac 2 AlMe 2 112.63 (15)°; 10 Fnac 2 AlMe 2 118.89(14)°; 16 Fnac 2 AlMe 2 120.77(7)°; 17 Fnac 2 AlMe 2 123.74(2)°]. Deviations from planarity (defined by N1, N2, C1, C3) are observed for the Al atom [0.8779(28) Å] and the γ ‐carbon atom [0.2163(33) Å] in complex 2 .…”

Section: Resultsmentioning

confidence: 81%

Synthesis of Homo‐ and Heteroleptic Al, Ga and Zn Complexes Containing (Per)fluorinated β‐Diketiminate Ligands

Huse

Ghosh

et al. 2020

Zeitschrift anorg allge chemie

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Alkane elimination reactions of equimolar amounts of 17Fnac2H (17Fnac2H = FC[C(CF3)NC6F5]2H) with ZnEt2 and AlMe3 as well as 16Fnac2H (16Fnac2H = HC[C(CF3)NC6F5]2H) with GaMe3 yielded the corresponding heteroleptic complexes of 17Fnac2ZnEt (1), 17Fnac2AlMe2 (2), and 16Fnac2GaMe2 (3), whereas reactions of two equivalents of 16Fnac2H and 17Fnac2H with either ZnEt2 or Cp*2Zn gave homoleptic ZnII complexes (16Fnac2)2Zn (4) and (17Fnac2)2Zn (5), respectively. 1–5 were characterized by IR and NMR spectroscopy (1H, 13C, 19F), elemental analysis and single‐crystal X‐ray diffraction.

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Section: Resultsmentioning

confidence: 81%

Synthesis of Homo‐ and Heteroleptic Al, Ga and Zn Complexes Containing (Per)fluorinated β‐Diketiminate Ligands

Huse

Ghosh

et al. 2020

Zeitschrift anorg allge chemie

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“…The Et-substituted catalysts 2 , 4 , and 6 are catalytically more active (see TOF values) than the Me-substituted complexes 1 , 3 , and 5 , respectively, typically reaching high conversions (>95%) within roughly half of the time. Comparable findings were reported for aluminum alkyl complexes, , and the enhanced catalytic activity of the Et-substituted complexes can be addressed to the slightly higher nucleophilicity of the Et compared to the Me group.…”

Section: Resultsmentioning

confidence: 65%

Cooperative Effect in Binuclear Zinc Catalysts in the ROP of Lactide

et al. 2022

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Me 3 and Et 4) and dimeric ketodiiminate zinc alkyl complexes [L 1 (H)ZnR] 2 (R = Me 5 and Et 6; L 1 = (Me 2 NC 2 H 4 NC (Me)CH) 2 CO, L 2 = (Me 2 NC 3 H 6 NC(Me)-CH) 2 CO) were synthesized and spectroscopically characterized ( 1 H and 13 C NMR and IR). Diffusion-ordered NMR spectroscopy and single-crystal X-ray diffraction analysis (1, 2, and 4−6) proved their monomeric (1−4) and dimeric (5 and 6) structures in solution and solid states. Their catalytic activity in the ring-opening polymerization of lactide was studied under various conditions and compared to mononuclear β-ketoimine zinc complexes 7−10. Initiation reactions of the Et-substituted complexes 2, 4, and 6 are faster than for the corresponding Me-substituted complexes 1, 3, and 5, and kinetic studies with catalyst 2 proved the first-order dependency on both the monomer and the catalyst concentration. Quantum chemical calculations revealed that the activation barriers for the addition of CH 3 − to L-LA via a mononuclear mechanism for the mono-( 7) and binuclear (1) Me-substituted and the corresponding MeO-substituted complexes 1-OMe and 7-OMe, which are regarded as model compounds of the "active" catalyst, are similar. However, while the binuclear mechanism for complex 1 is slightly higher in energy than for the mononuclear mechanism, the binuclear pathway for the MeO-substituted complex 1-OMe is favored, clearly proving the beneficial cooperative effect between the two adjacent zinc atoms.

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“…The AlÀ Et complexes could be expected to be more Brønsted basic (favouring alcoholysis) and nucleophilic (favouring LA ring-opening) than their AlÀ Me counterparts (Figure S44); previously reported AlÀ Et complexes have outperformed their Me-substituted analogues. [36][37][38] Indeed, in contrast to the AlÀ Me analogues, L1(AlEt) 3 is active in the absence of BnOH albeit with poor initiation efficiency as indicated by polymers of unexpectedly high molecular weight and relatively broad dispersity (entries 3 and 9, Table 1). In the presence of BnOH, L1(AlEt) 3 and L1(AlMe) 3 showed similar activities (Table 1, entries 1 and 7).…”

Section: Resultsmentioning

confidence: 99%

To Be or Not To Be… Cooperative? Trimetallic Catalysts for the Ring‐Opening Polymerisation of Cyclic Esters

Lowy,

Abdul Rahman,

Nichol

et al. 2024

ChemCatChem

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Multimetallic catalysts have emerged as a promising route to enhance catalyst performance in cyclic ester ring‐opening polymerisation (ROP), as these complexes can outperform the monometallic analogues in terms of reactivity and/or polymerisation control. Such enhancements are often attributed to “multimetallic cooperativity”, yet the origins of this cooperativity often remain unclear. Here, we report the synthesis and characterisation of two trimetallic Al‐salen complexes (L1(AlMe)3 and L1(AlEt)3), containing three Al‐salen subunits in close proximity, and their monometallic analogues (L2(AlMe) and L2(AlEt)). These complexes have been applied as catalysts for cyclic ester ROP under a range of conditions, to probe their potential for cooperative behaviour. Trimetallic L1(AlMe)3 and L1(AlEt)3 both display high activities in rac‐lactide ROP, giving kobs values of up to 11 x 10‐3 min‐1. Yet careful benchmarking against the monometallic complexes reveals that whether these systems display multimetallic cooperativity or not depends upon the reaction conditions. Detailed kinetic and spectroscopic studies into the origins of cooperativity revealed that the neighbouring metals play a key role in the initiation step, rather than propagation. Overall, these studies highlight the importance of understanding the reaction conditions in order to accurately define whether a catalyst displays multimetallic cooperativity.

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Synthesis and Characterization of β‐Diketiminate Aluminum Compounds and Their Use in the Ring‐Opening Polymerization of ε‐Caprolactone

Cited by 9 publications

References 53 publications

Synthesis of Homo‐ and Heteroleptic Al, Ga and Zn Complexes Containing (Per)fluorinated β‐Diketiminate Ligands

Synthesis of Homo‐ and Heteroleptic Al, Ga and Zn Complexes Containing (Per)fluorinated β‐Diketiminate Ligands

Cooperative Effect in Binuclear Zinc Catalysts in the ROP of Lactide

To Be or Not To Be… Cooperative? Trimetallic Catalysts for the Ring‐Opening Polymerisation of Cyclic Esters

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